A common method of collecting a sample for analysis by gas chromatography is “solid phase micro-extraction,” or SPME. In this method, a sorbent material is exposed to an environment containing analytes, causing some of the analytes to be adsorbed onto the sorbent material. The sorbent material is then transferred to a container, connected to the injection port of the gas chromatograph, and heated so as to cause the adsorbed analytes to be desorbed and carried by an inert carrier gas into the gas chromatograph. Typically, the sorbent material is indirectly heated by conventional thermal transfer, whereby the container is directly heated, and the heat is allowed to flow into the sorbent material indirectly by thermal conduction.
This indirect heating desorption process can be slow and inefficient, and attempts to speed up the process by applying more heat may lead to thermal degradation and rearrangement of the analytes. Also, desorption utilizing indirect thermal conduction heating can decrease the uniformity of the analyte retrieval, thereby leading to inaccurate quantitative analysis, especially when applied to a carbonaceous sorbent material that has poor heat conductivity, and particularly for large, high boiling point analytes. Frequently, the sorbent material is configured in a long, narrow bed to avoid breakthrough of the analytes. This geometry greatly compounds the difficulty of obtaining quantitative results.
What is needed, therefore, is an apparatus and method for rapid desorption of analytes from carbonaceous sorbent materials with reduced re-adsorption and correspondingly improved quantitative results, and with reduced thermal degradation and rearrangement of the adsorbed analytes.